A skipper was startled to spot a two-metre great white shark near his boat at a marina south of Adelaide on the Fleurieu Peninsula.

Jarrod Glaister, the owner and captain of Southern Fishing Charters, was performing upkeep on his vessel at Marina St Vincent yesterday morning when he noticed something in the water.

“We thought it was a dolphin at first, but then realised it was a six, seven foot white,” he told 9news.com.au.

Since March, a microalgae bloom has led to discolored water and foam appearing along sections of the Fleurieu Peninsula, Kangaroo Island, and the southern coast of the Yorke Peninsula.

It’s caused mass deaths of marine life, which have been washed ashore on coasts. 

The algae are not harmful to humans, but exposure can cause temporary skin and eye irritation and respiratory symptoms.

Experts believe the bloom is being caused by rising sea temperatures, which are 2.5 degrees warmer than usual, and calm conditions.

Government agencies are monitoring the situation, but advise that nothing can be done to dilute or dissipate the bloom naturally. 

The last time the state recorded a similar event of this magnitude was in Coffin Bay in 2014.